1. Field of the Invention
The present invention generally relates to a storage device for storing binary data and, more particularly, to a storage device equipped with a magnetoresistive element presenting hysteresis characteristics in the relationship between a magnetic field and a volume resistivity change rate (MR ratio).
2. Description of the Related Art
In the field of computers and communication systems which deal with digital data, storage devices for storing binary data are required. Such a storage device is so constituted as to retain either temporarily or permanently the difference of some physical states such as magnetic ones.
In the conventional storage devices known heretofore, there is a type capable of storing data in accordance with the presence or absence of electric charge accumulated in a capacitor, as represented by a dynamic random access memory (DRAM). However, a DRAM has a disadvantage that the data stored therein is lost unless an overwrite operation termed refresh is performed continuously. That is, there exists a problem of nonvolatility.
Any of magnetic recording apparatus represented by a magnetic disk apparatus is nonvolatile, since data is recorded by changing the direction of magnetization of a magnetic substance. But a rotary mechanism, a read/write head positioning mechanism and so forth are necessary therein, and a long time is taken for positioning the head and transferring the data. Consequently, a considerable time is required for writing and reading the data.
A flash memory is known as a nonvolatile semiconductor storage device. Since an overwrite operation is impossible in a flash memory, it is necessary to perform an erase operation first and then a write operation, hence inducing a disadvantage that this type is not suited for high-speed repetitive recording purpose. And the ensured number of times of writing is no more than 1.times.10.sup.5 or so.
In Japanese Patent Laid-open Nos. Hei 1 (1989)-178190, Hei 1 (1989)-178191 and Sho 61 (1986)-153897, there is disclosed a method of recording data on a magnetic medium by causing a current flow in intersecting striped superconductors, and detecting the direction of magnetization by adjacent magnetoresistive elements. However, in this method where superconductors are required, there exist some problems including that it is unemployable at normal temperature, and the production cost of the apparatus is increased. Furthermore, there is another disadvantage that both a recording magnetic medium and reading magnetoresistive elements need to be prepared.
In the thesis titled Magnetic Thin Film (by Miyazaki, Tohoku University), there is described a testing method according to which a thin film is interposed between mutually orthogonal conductors via insulator layers, and the magnetic characteristic of the thin film is measured by a tunnel current detection means. Although this method is capable of realizing a device of a simplified structure, it is difficult to apply the method to a practical recorder since the change range of the resistance value is excessively small due to utilization of the tunnel current. In addition, the magnetic field generation efficiency to the current is low as the magnetic field of the orthogonal lines is utilized directly.